Hydrogels have been used for various purposes including the encapsulation of biological material such as organelles, enzymes, microorganisms and plant cells. See, e.g. K. Redenbaugh, D. Slade, P. Viss and M. Kossler, "Artificial seeds: encapsulation of somatic embryos," Forest and Crop Biotechnology--Progress and Prospects, F. Valentine, ed., Springer--Verlag, New York, pp. 400-419. U.S. Pat. Nos. 4,615,883 and 4,701,326 disclose the use of such structures to encapsulate nematodes and U.S. Pat. Nos. 4,562,663 and 4,583,320 describe systems utilizing encapsulated plant meristematic tissue.
The gel capsules disclosed, however, adhere together due to the sticky, adhesive nature of the capsule surface. As a result, capsules are not easily singulated into discrete units and are not readily flowable through automated planting machinery.
Mechanized planting requires the flow of individual capsules through the machinery used. The presence of aggregates or clumps tends to jam the feeding mechanism of the machinery and prevents mass handling of encapsulated plant units.
U.S. Pat. No. 4,715,143 discloses a method of singulation of hydrogel capsules using a membrane composed of various organic compounds or mixes of organic and inorganic compounds. The membrane compounds are first dissolved in various organic solvents and capsules are dipped into the membrane solution. The membrane produced forms a thin, continuous barrier over the capsule. This membrane suffers from several drawbacks. Capsules must be pre-treated before dipping in the membrane solution. The membrane is complicated to prepare and requires the exposure of encapsulated organisms to potentially toxic solutions. Further, the membrane components are subject to contamination during extended storage periods. In addition, the continuous barrier inhibits solute passage essential for leaching growth inhibitors and impedes gas exchange from the organism to the environment.
An alternative to using a solvent-based membrane system is the use of a hydrophobic powdered coating to allow for singulation of hydrogel capsules without the use of solvents or other organic compounds.
Hydrophobic powders have been used in various agricultural applications. U.S. Pat. No. 3,710,510 describes the use of pyrogenic silicas and metallic oxides dispersed in solution to form fine droplets of liquid coated with powder. These droplets can be added to planting beds of mineral solids such as sand, vermiculite, perlite and clays to accelerate seed germination rate and plant growth. U.S. Pat. No. 4,004,368 is a modification of this method for adhering the hydrophobic powders onto larger, heavier particles within the planting bed. Neither of these patents contemplate the use of powders for capsule singulation purposes.
Hydrophobic powders have also been used for coating seeds. U.S. Pat. No. 4,438,593 discloses the use of a particulate hydrophobe to enhance the effectiveness of anti-fungal agents against soil pathogens, but does not teach of the use of such powders for coating hydrogel capsules. Additionally, U.S. Pat. Nos. 4,583,320 and 4,715,143 describe the use of certain hydrophobic substances as a component of the hydrogel capsule. However, none of these references disclose the use of such substances as an adjunct to surround the hydrogel capsule to prevent capsule adhesion.
Accordingly, an object of this invention is to provide a technique whereby hydrogel capsules are coated with hydrophobic powders for singulation purposes.
Another object of the present invention is to provide a powder that does not absorb water and enables capsules to be flowable, single units.
Yet another object of the instant invention is to provide a powder coating that retains its ability to singulate capsules after extended storage periods.
A further object of the subject invention is to provide a coating that will not be degraded nor subject to contamination under septic storage conditions.
A still further object of the invention is the use of powders that are innocuous and non-toxic to the plant tissue encased within the capsules.